1. Field of the Invention
The present invention relates to an exhaust purification device that collects particulate matters in exhaust gas with a particulate filter provided in an exhaust passage of an internal combustion engine and that combusts the collected particulate matters to regenerate the particulate filter.
2. Description of Related Art
In recent years, an exhaust purification device that performs treatment of exhaust gas discharged from an internal combustion engine with a catalyst or a filter to reduce emission of harmful components is becoming more and more important. For example, a known exhaust purification device has a particulate filter provided in an exhaust passage for collecting particulate matters discharged from a diesel engine (for example, as described in Patent document 1: JP-A-2004-301013). The particulate matters deposited in the particulate filter are regularly combusted and removed to regenerate the particulate filter, whereby the particulate filter can be continuously used.
The particulate filter is regenerated by increasing the temperature of the particulate filter to temperature (for example, 600 degrees C. or over), at which the particulate matters combust, when a particulate matter deposition quantity exceeds a predetermined value. For example, the particulate matter deposition quantity is computed on the basis of differential pressure between an upstream side and a downstream side of the particulate filter.
However, fuel consumption is deteriorated if the temperature of the particulate filter is increased to combust the particulate matters by well-known methods such as a post-injection of injecting fuel at a later crank angle than a main injection, which produces a main engine output, or throttling of an intake air.
When the increased temperature of the particulate filter is excessively low, combustion speed of the particulate matters becomes slow and hence the time required to regenerate the particulate filter becomes long and hence the fuel consumption is further deteriorated. Conversely, as the increased temperature of the particulate filter is increased more, the combustion speed of the particulate matters becomes faster and hence the regeneration of the particulate filter is finished in a shorter time, so the deterioration in the fuel consumption accompanying the regeneration of the particulate filter is reduced. However, when the temperature of the particulate filter is increased to excessively high temperature, the particulate filter may be damaged or an oxidation catalyst supported by the particulate filter may be degraded.
In order to prevent the deterioration in the fuel consumption and to regenerate the particulate filter safely, the temperature of the particulate filter needs to be maintained near specified temperature. The technology described in Patent document 1 aims to control the increased temperature of the particulate filter to specified temperature with high accuracy by switching between execution and stoppage of temperature increase operation by a temperature increase device in accordance with a time ratio.
However, if the execution and the stoppage by the temperature increase operation of the temperature increase device are switched in accordance with the time ratio as described in Patent document 1, there is a possibility that the engine output fluctuates due to the switching between the execution and the stoppage of temperature increase operation by the temperature increase device, depending on the operation state of the internal combustion engine.